I have no idea if people besides me have similar problems but , if not, this report could still be interesting reading.

I've noticed a tendency to play flat and the condition may have gotten worse over the past year.  Now, this sounds rather dumb.  If I know and hear "flat" why not just play "sharp"?  What other gremlins could be at work?

I probably have fixed the problem and I will tell how I did that.  First, there was the issue of left elbow position.  I did not have the elbow far enough to the right.  This then had the tendency to pull the left hand "flat" …… remember, I said not by much.  The pinkie reach is very limited by hand position and maybe less for the other fingers.
Then, I noticed the use of the left hand and fingers.  Intonation improved dramatically by using just the finger tips.  I'm sure that this allows me to "rock" the finger position into tune.  But again, all this is related to where the elbow is placed and how well the hand is positioned over the strings ready for more accurate pitch and more chance to correct.

I played for half the day with all kinds of music and two violins and I'm convinced that a big improvement took place.  Now I have another thing to add to my "pre-flight" check list.  

I can not say what all the gremlins may be that can ambush a student but they may occur anywhere